It is often desirable to use a single measuring device, such as a weighing scale, to perform a wide range of measurements. For instance, a postal scale may be used to weigh very light items such as letters weighing one ounce, and also relatively heavy items such as packages weighing several pounds or more. Typically the light items are to be weighed quite accurately; for letter mail accuracy to the nearest 1/32 ounce is desired. Less accurate weighing is usually required for the heavier items. It is known to provide weighing scales with two or more weighing ranges: a highly accurate low range for weighing light items and one or more less accurate high ranges for heavier items. As previously proposed, multirange scales have included two or more load cells, mechanically coupled in tandem in such a manner that the item to be weighed is supported by all of the load cells. One load cell is suitable for providing the low weighing range and the other load cell or cells provide the higher range or ranges. Such scales also include electronic componentry for receiving, conditioning and processing the outputs of all of the load cells. Patents disclosing such scales include U.S. Pat. No. 4,375,243 (to Doll), U.S. Pat. No. 4,690,230 (to Uchimura et al.), U.S. Pat. No. 4,778,016 (to Uchimura et al.) and U.S. Pat. No. 4,632,198 (to Uchimura).
A number of disadvantages attend multiple load cell scales. For example, the cost of producing the scale is increased by the cost of the additional load cell or cells and also by the cost of the additional electronic components associated with each load cell. Additional costs result from the structure required for mounting the additional load cell or cells.
It is therefore desirable to provide a multiple range measuring device, such as a weighing cell, that uses a single transducer.